A Printed Rampart-Line Antenna with a Dielectric Superstrate for UHF RFID Applications Benjamin D. Braaten Gregory J. Owen Dustin Vaselaar Robert M. Nelson Cherish Bauer-Reich Jacob Glower Brian Morlock (PacketDigital LLC) Michael Reich (CNSE) Aaron Reinholz (CNSE) North Dakota State University

Topics  Introduction  Background  Design Process  Design Example  Conclusion North Dakota State University

Introduction  Interest in RFID has recently grown tremendously in many areas [1]-[5]:  supply chain management [6]-[8]  RFID security [9]-[10]  UHF antenna design [11]  back-scattering analysis [12]-[14]  Types of systems [1]  passive  semi-passive  active North Dakota State University

Introduction  Our work focused on the antenna design of a passive RFID tag.  On a passive tag the antenna is typically connected directly to the rectifier.  thus antenna impedance and rectifier impedance directly effect the read range  Antenna characteristics (gain, input impedance and resonant frequency) can be effected by nearby conducting and non-conducting objects [15]-[21]:  Isotropic and anisotropic superstrates  Surface placement of tag  Other RFID tags North Dakota State University

Introduction  Several advantages are gained by using a superstrate [18]:  Protection against heat, physical damage, and the environment (moisture, sun)  Several examples include:  Electronic car tolling [22]  Livestock tracking [23]-[24] North Dakota State University

Background  The max theoretical read range of a passive RFID tag can be written as (using Friis’s eqn.) [25]: where North Dakota State University

Background The layout region can contain many different designs and be located on many different surfaces [27]-[38]: North Dakota State University

Antenna Design Process First start with determining the electrical length of each segment of a rampart line antenna. North Dakota State University

Antenna Design Process The length of the kth segment is written as: This then gives the entire length of the dipole as:

Antenna Design Process For the rest of this paper we assumed the following symmetry: Same length North Dakota State University

Antenna Design Process Next, start with the rampart line antenna and use a CAD program to determine N: Design for the application Located here

Antenna Design Process Then define pivot points to fit the antenna on the space provided and define an inductive loop for input impedance:

Antenna Design Results  Operating frequency of 920MHz  60mil substrate with permittivity of 4.25  60mil superstrate with permittivity of 4.0  Results in N=12  Gr=4.3dBi North Dakota State University

Antenna Design Results  Layout a): (H=2985mils and W=1522mils)  Gr=2.62dBi  Zin= j  Layout b): (H=2746mils and W=1540mils)  Gr=2.97dBi  Zin=36.93+j

Antenna Design Results  The printed boards on 5mil FR4 and BT substrate, resp.  Type F and Type PFC epoxy was used to attach straps  Cured at 50C for 8hrs.  Both layouts with both substrates and epoxy were tested. North Dakota State University

Measurement Results The test structure

Measurement Results The read range results

Measurement Results Several normalized-pattern results EthetaEphi

Measurement Results Simulated gain and input impedance results: North Dakota State University

Conclusion  A design process based on a Rampart line antenna has been presented  Yields antennas with:  high gain,  flexible impedance values,  high space filling and  constant impedance  Two designs have been validated with measurement and shows to yield a comparable read range to tags applied to other applications. North Dakota State University

Questions Thank you for listening North Dakota State University

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